The expected move is the price range the options market is pricing for a stock over a chosen horizon. The one standard deviation form is stock price times implied volatility times the square root of time: about 68 percent of outcomes fall inside it under the model, and about 95 percent fall inside twice that range.
Model arithmetic on the numbers entered above, for illustration. It is not a forecast of any stock's actual range.
Expected move = stock price x implied volatility x the square root of (days / 365). Implied volatility is quoted annualized, so the square root of time rescales it to the horizon in question. This is the same volatility-cone arithmetic behind the price cones on trading platforms and behind strike-selection heuristics like placing short strikes beyond the one standard deviation range.
A $100 stock with implied volatility of 30 and 30 days ahead: 100 x 0.30 x sqrt(30/365) = 100 x 0.30 x 0.2867 = about $8.60. The one standard deviation range is roughly $91.40 to $108.60, and the two standard deviation range is roughly $82.80 to $117.20. Under the model, about 68 percent of outcomes land inside the first range and about 95 percent inside the second.
The calculation reads the options market's own price of movement; it is descriptive, not predictive. Three limits matter in practice:
Premium-selling rule sets use the expected move to judge strike distance: a short strike beyond one standard deviation corresponds roughly to a 16 delta under the same model. The price cone article shows the same arithmetic drawn over time rather than at a single horizon.